Triggering power headroom reporting in TDD system

Abstract

The present invention relates to a wireless communication system. More specifically, the present invention relates to triggering conditions for power headroom reporting (PHR) in a wireless network employing TDD scheme. According to one aspect of the present invention, the a user equipment (UE), receives information on a first time division duplex (TDD) uplink/downlink (UL/DL) subframe configuration, and information on a second TDD UL/DL subframe configuration informing the UE of a change from the first TDD UL/DL subframe configuration. And, the UE triggers a power headroom reporting (PHR), when the information on the second TDD UL/DL subframe configuration is received.

The invention claimed is: 
     
       1. A method of communicating with a network by a user equipment (UE), the method comprising:
 receiving information on a first time division duplex (TDD) uplink/downlink (UL/DL) subframe configuration with a first threshold value; 
 receiving information on a second TDD UL/DL subframe configuration with a second threshold value informing the UE of a change from the first TDD UL/DL subframe configuration; 
 triggering a power headroom reporting (PHR), when a required power backoff according to the second TDD UL/DL subframe configuration has changed more than the second threshold value; and 
 transmitting the PHR to the network if the PHR is triggered, 
 wherein the PHR comprises:
 an identifier informing the network that the PHR is for a specific TDD UL/DL subframe configuration, and 
 a power headroom (PH) value of the specific TDD UL/DL subframe configuration, and 
 
 wherein the information on the second TDD UL/DL subframe configuration is received via a Radio Resource Control (RRC) message including multiple TDD UL/DL subframe configurations for the second TDD UL/DL subframe configuration. 
 
     
     
       2. The method of  claim 1 , wherein the information on the second TDD UL/DL subframe configuration is received via a physical signaling. 
     
     
       3. The method of  claim 2 , wherein the information on the second TDD UL/DL subframe configuration comprises an indication to use a specific TDD UL/DL, subframe configuration as the second TDD UL/DL subframe configuration. 
     
     
       4. The method of  claim 1 , wherein the first TDD UL/DL subframe configuration is received via system information. 
     
     
       5. The method of  claim 1 , wherein the second TDD UL/DL subframe configuration is more frequently signaled than the first TDD UL/DL, subframe configuration. 
     
     
       6. The method of  claim 1 , wherein the second TDD UL/DL subframe configuration allocates more downlink subframes than the first TDD UL/DL subframe configuration. 
     
     
       7. A user equipment (UE) for communicating with a network, the UE comprising:
 a transceiver configured to receive information on a first time division duplex (TDD) uplink/downlink (UL/DL) subframe configuration with a first threshold value, and information on a second TDD UL/DL subframe configuration with a second threshold value informing the UE of a change from the first TDD UL/DL subframe configuration; and 
 a processor connected to the transceiver and configured to trigger a power headroom reporting (PHR), when a required power backoff according to the second TDD UL/DL subframe configuration has changed more than the second threshold value, 
 wherein the transceiver is further configured to transmit the PHR to the network if the PHR is triggered, and 
 wherein the PHR comprises:
 an identifier informing the network that the PHR is for a specific TDD UL/DL subframe configuration, and 
 a power headroom (PH) value of the specific TDD UL/DL subframe configuration, and 
 
 wherein the information on the second TDD UL/DL subframe configuration is received via a Radio Resource Control (RRC) message including multiple TDD UL/DL subframe configurations for the second TDD UL/DL subframe configuration. 
 
     
     
       8. The UE of  claim 7 , wherein the information on the second TDD UL/DL subframe configuration is received via a physical signaling. 
     
     
       9. The UE of  claim 8 , wherein the information on the second TDD UL/DL subframe configuration comprises an indication to use a specific TDD UL/DL subframe configuration as the second TDD UL/DL subframe configuration. 
     
     
       10. The UE of  claim 7 , wherein the first TDD UL/DL subframe configuration is received via system information. 
     
     
       11. The UE of  claim 7 , wherein the second TDD UL/DL subframe configuration allocates more downlink subframes than the first TDD UL/DL subframe configuration.